Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view for a display screen with a graphic user interface showing my new design; and,

FIG. 2 is a front view of a second embodiment thereof.

The broken lines around the Figures showing a display screen or portion thereof are included for the purpose of illustrating environmental structure. The broken line showings of the text, numbers, symbols, function marks, and images in Figures are included for the purpose of illustrating portions of the display screen with a graphic user interface. The broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 